(a) Field of the Invention
The present invention relates to a planetary gear set, and more particularly, to the planetary gear set in which a coupling structure of a pinion shaft and a carrier is improved.
(b) Description of the Related Art
Generally, a planetary gear set includes a carrier assembly connecting a sun gear, a ring gear, and a pinion gear with each other. The carrier assembly further includes a carrier and a pinion-shaft fixed to the carrier.
There are several methods for fixing the pinion shaft to the carrier. A typical method is that holes are made at some portions of the pinion shaft and the carrier, and a pin is inserted into the holes.
FIG. 3 is a partial cross-sectional view of a planetary gear set of a related art.
Referring to FIG. 3, a planetary gear set 10 includes pinion shaft 12, pinion gear 16, and carriers 30a and 30b. A bearing 32 is interposed between an interior circumference of the pinion gear 16 and an exterior circumference of the pinion shaft 12, and the pinion gear 16 rotates about a center axis of the pinion shaft 12. Also the carriers 30a and 30b are engaged to distal ends of the pinion shaft 12 respectively, and a spline 28 is formed on an exterior circumference of the carrier 30b. 
A first pin hole 22a is formed in the right end portion of the pinion shaft 12, and the carrier 30a is provided at a portion where the first pin hole 22a is formed. As shown, a second pin hole 22b is also formed in the carrier 30a, 
A fixing pin 20 is inserted into the first and the second pin holes 22a and 22b together. Thus the pinion shaft 12 and the carrier 30a are engaged with each other.
However, since the fixing pin 20 is forcefully fitted when the fixing pin 20 is inserted to the pin holes 22a and 22b, it is difficult to insert the fixing pin 20 in the pin holes 22a and 22b. 
In addition, there is a problem in that residual stress occurs between the fixing pin 20 and the pin holes 22a and 22b. If residual stress is increased, the size of components around the fixing pin 20 or the pin holes 22a and 22b can be changed. Further, it is difficult to draw out the fixing pin 20 from the pin holes so as to disassemble the pinion shaft 12 from the carrier 30a. 
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.